Etching Method and Etching Apparatus

This application is a bypass continuation application of International Patent Application No. PCT/JP2024/003640 having an international filing date of Feb. 5, 2024 and designating the United States, the international application being based upon and claiming the benefit of priority from Japanese Patent Application No. 2023-038892, filed on Mar. 13, 2023, the entire contents of which are incorporated herein by reference.

The present disclosure relates to an etching method and an etching apparatus.

In a manufacturing process of a semiconductor device, etching is performed on a silicon oxide film formed on a substrate such as a semiconductor wafer (hereinafter referred to as “wafer”). Patent Document 1 discloses that etching is performed by supplying an amine gas to the silicon oxide film.

Patent Document 1: International Patent Pamphlet No. WO2020/054476A1

According to one embodiment of the present disclosure, there is provided an etching method including: etching a silicon oxide film by supplying a halogen-containing gas, an ammonia gas, and an amine gas as etching gases to a substrate including the silicon oxide film formed on a surface of the substrate.

Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, systems, and components have not been described in detail so as not to unnecessarily obscure aspects of the various embodiments.

3 11 12 12 14 12 13 12 12 14 13 1 FIG. An embodiment (Example) of an etching method of the present disclosure is described. To outline the etching method, a halogen-containing gas, an ammonia (NH) gas, and an amine gas are supplied as etching gases to a substrate, namely, a wafer W, thereby etching a silicon oxide (SiOx) filmon a surface of the wafer W. As illustrated in, a Si filmis formed on the surface of the wafer W, and a groove is formed in the Si film. Thus, a recessthat opens in a thickness direction of the wafer W is formed by the Si filmand an underlying filmformed below the Si film, and the Si filmis configured as a sidewall forming the recess. In addition, the underlying filmis omitted in some of the drawings described later.

11 14 11 12 11 11 14 Further, the SiOx filmis formed in the recess. Using the aforementioned etching gases, among silicon-containing films exposed on the surface of the wafer W, namely, the SiOx filmand the Si film, the SiOx filmis selectively etched. The etching is performed such that a portion of the SiOx filmremains in the recessafter the etching. In addition, no plasma is created around the wafer W in performing this etching.

11 In a more detailed description of the etching in Example, a desired amount of the SiOx filmis etched by repeating the supply of the etching gases to the wafer W and sublimation (including vaporization) of reaction products while stopping the supply of the etching gases to the wafer W. In addition, in Example, a hydrogen fluoride (HF) gas may be used as a halogen-containing gas, which is one of the etching gases.

3 3 11 14 As described above, the etching gases include an NHgas and an amine gas, each being a basic gas. The use of both the NHgas and the amine gas enables a top surface (surface) of the SiOx filmremaining in the recessafter the etching to have relatively high flatness, thereby preventing degradation in performance of a semiconductor device manufactured from the wafer W due to poor flatness. In addition, in Example, a HF gas may be used as the halogen-containing gas, and a trimethylamine (TMA) gas is used as the amine gas.

3 3 2 3 FIGS.A toB 11 21 11 To clearly show effects of the etching gases in Example, processing in Comparative Examples is first described below. Processing using a HF gas and NHgas as etching gases is referred to as Comparative Example 1, and processing using a HF gas and TMA gas as etching gases is referred to as Comparative Example 2. First, etching in Comparative Example 1 is described.are vertical cross-sectional views of the wafer W illustrating changes in the SiOx filmthat are estimated to occur during the processing of Comparative Example 1. In the drawings, the etching gases including the HF gas and NHgas are illustrated as an etching gas. In addition, unless otherwise specified in the following description, references to left and right ends and a lateral central portion in relation to the SiOx filmrefer to left and right ends and a lateral central portion in a vertical cross-sectional view.

21 11 14 21 15 15 11 2 FIG.A 2 FIG.B 4 6 When the etching gasis supplied to the wafer W adjusted to a predetermined temperature (), a surface of the SiOx filmin the recessreacts with the etching gasto form a layercontaining ammonium fluorosilicate [(NH)SiF: AFS] as reaction products. An unevenness in a thickness of the AFS layeroccurs between the left and right ends and the central portion on the SiOx film().

21 11 12 12 15 21 12 More specifically, the etching gasis supplied more to the lateral central portion of the SiOx film(i.e., a region relatively distant from an interface with the Si film) than to the left and right ends (i.e., a region near the interface with the Si film). Therefore, the AFS layerbecomes thicker at the lateral central portion than at the left and right ends. In addition, the reason for this variation in a supply amount of the etching gasacross various regions of the SiOx film is due to the Si film, which is described in detail in Comparative Example 2.

11 21 15 11 11 21 15 11 11 11 15 12 15 21 15 11 2 FIG.C 2 FIG.D The lateral central portion of the SiOx filmtends to less come into contact with the etching gasdue to the formation of the relatively thick AFS layerat the lateral central portion of the SiOx film. In contrast, the left and right ends of the SiOx filmmore easily come into contact with the etching gassince the thickness of the AFS layerformed at the left and right ends of the SiOx filmis relatively thin. Therefore, the reaction progresses more at the left and right ends than at the lateral central portion of the SiOx film, leveling surface heights of the SiOx filmbetween the lateral central portion and the left and right ends (). However, as illustrated in evaluation tests described below, AFS has low adsorbability to Si but high adsorbability to itself, leading to aggregation. Among AFS forming the AFS layer, AFS near the interface with the Si filmdesorbs from the AFS layer. That is, if the supply of the etching gascontinues, the thickness of the AFS layeron the left and right ends of the SiOx filmdecreases ().

15 21 11 15 11 21 11 15 21 11 11 3 FIG.A 3 FIG.B As the thickness of the AFS layerdecreases in this manner, the reaction with the etching gasprogresses more readily at the left and right ends of the SiOx film, but is relatively prevented at the lateral central portion. Then, the AFS layerbecomes thick again over both the left and right ends and the lateral central portion of the SiOx film, which hinders contact with the etching gasand stops the reaction (). At the time of the stopping of the reaction, the surface of the SiOx filmhas a convex shape with the lateral central portion higher than the left and right ends since the reaction progressed as described so far. Then, although the AFS layeris removed by adjusting a temperature of the wafer W and exhausting an atmosphere around the wafer W after stopping the supply of the etching gasto the wafer W, the SiOx filmretains the convex shape (). Accordingly, the surface flatness of the SiOx filmis relatively low.

4 4 FIGS.A toD 4 4 FIGS.A toD 4 4 FIGS.A toD 4 4 FIGS.A toD 4 FIG.A 4 FIG.B 11 22 22 11 14 22 16 16 16 22 11 16 3 Next, etching in Comparative Example 2 is described with reference towith a focus on differences from Comparative Example 1.are vertical cross-sectional views of the wafer W illustrating changes in the SiOx filmthat are estimated to occur during the processing of Comparative Example 2.are vertical cross-sectional views illustrating changes in the wafer W that are estimated to occur during this etching. In, the etching gases including a HF gas and TMA gas are illustrated as an etching gas. When the etching gasis supplied to the wafer W adjusted to a predetermined temperature (), the surface of the SiOx filmin the recessreacts with the etching gas, and a reaction productis generated. The reaction producthas a lower sublimation temperature compared to the AFS generated from the NHgas. Accordingly, the reaction productsublimates quickly after its generation, and contact between the etching gasand the SiOx filmis unlikely to be hindered by the reaction product().

22 14 22 12 11 22 12 22 11 11 11 11 4 FIG.C 4 FIG.D In addition, a portion of the etching gasis supplied downward along an opening direction of the recess, while another portion is supplied obliquely with respect to the opening direction. The portion of the etching gassupplied in this manner bounces off the Si filmwhile moving downward, thereby being supplied to the lateral central portion of the SiOx filmin the vertical cross-sectional view. That is, molecules of the etching gasare directly supplied to the lateral central portion, or molecules that have bounced off the Si filmare supplied to the lateral central portion. In other words, a relatively large number of molecules of the etching gascollide with the lateral central portion of the SiOx film, but due to the above-described bouncing, molecules are less likely to collide with the left and right ends. Consequently, etching of the SiOx filmprogresses more significantly in the central portion than in the left and right ends due to a difference in collision probabilities of the molecules (). Therefore, the surface of the SiOx filmafter completion of the etching has a concave shape with the lateral central portion lower than the left and right ends in the vertical cross-sectional view (). Accordingly, the surface flatness of the SiOx filmis relatively low.

5 FIG. 2 4 FIGS.A toD 5 FIG. 5 FIG. 5 FIG. 11 11 3 3 3 is a conceptual diagram illustrating etching in Example. The left side of the drawing illustrates the SiOx filmetched using one of an NHgas and a TMA gas, as described in. Sublimabilities of the generated reaction products differ depending on whether the NHgas or the TMA gas is used as the etching gas as described so far, affecting whether the central portion or the peripheral edge portion of the SiOx filmbecomes higher after the etching. In Example, all of these gases are used. By doing so, a balance between the actions of these gases may be achieved, thereby preventing the lateral central portion from becoming higher than the ends as illustrated in the lower right section ofcompared to the case of using the NHgas alone, or preventing the left and right ends from becoming higher than the central portion as illustrated in the upper right section ofcompared to the case of using the TMA gas alone. Further, as illustrated in the middle right section of, it is also possible to equalize the height between the lateral central portion and the left and right ends.

6 6 FIGS.A toD 7 FIG. 7 FIG. The etching step in Example is described with reference to vertical cross-sectional views ofand a timing chart of. The timing chart illustrates timings at which gases are supplied respectively to the wafer W. As described later, the wafer W is stored and processed in a processing container, andillustrates supply and stop timings of the respective gases into the processing container. Further, an interior of the processing container is exhausted to create a vacuum atmosphere at a predetermined pressure, and the wafer W adjusted to a predetermined temperature is etched.

3 3 3 1 21 22 21 11 15 15 15 15 11 2 4 FIGS.A toD 6 FIG.A A HF gas, NHgas, and TMA gas are supplied as etching gases to the wafer W in the processing container (at time tin the chart). That is, the respective gases illustrated as the etching gasesandinare supplied to the wafer W (). Among these gases, the HF gas and NHgas (etching gas) act on the SiOx film, forming the AFS layeras described in Comparative Example 1. However, since a basic gas includes the TMA gas, a partial pressure of the NHgas may be relatively reduced, thereby allowing the thickness of the AFS layerto be relatively thin. With the AFS layerbeing relatively thin in this way, the respective etching gases may pass through the AFS layerand act on the SiOx film.

15 15 11 11 22 11 12 16 21 22 The AFS layeris formed such that the thickness in the lateral central portion is greater than the thickness in the left and right ends, as described in Comparative Example 1. Accordingly, regarding a shielding effect of the AFS layeragainst the etching gases on the SiOx film, the effect is greater in the central portion than in the left and right ends of the SiOx film, resulting in prevention of the etching in the central portion. However, as described in Comparative Example 2, the collision probability of the etching gasin the lateral central portion of the SiOx filmis relatively high due to the presence of the Si film, leading to the generation of the reaction product, which then sublimates. In addition, the etching gasalso collides relatively more frequently with the lateral central portion, similarly to the etching gas.

15 11 2 15 16 11 11 6 FIG.B 6 FIG.C 3 In this way, a balance is achieved between the shielding effect of the AFS layerand the difference in the collision probabilities of the respective gases, so that the SiOx filmundergoes highly uniform modification across both the lateral central portion and the ends (). Then, the supply of each of the HF gas, NHgas, and TMA gas to the wafer W is stopped (at time t). Then, the wafer W is subjected to temperature adjustment and the processing container is exhausted, causing the AFS layerto sublimate and be removed (). In addition, if other reaction products such as the reaction productremain on the SiOx film, they also sublimate and are removed, exposing the surface of the SiOx film.

2 3 11 4 11 11 4 5 3 3 After a predetermined period has passed from time t, the etching gases, i.e., the HF gas, NHgas, and TMA gas are again supplied to the wafer W (at time t), and react with the SiOx film. After that, the supply of the etching gases to the wafer W is stopped (at time t), and the reaction products on the SiOx filmare removed by sublimation of the reaction products and exhaust of the processing container, whereby the etching progresses and the SiOx filmis exposed. Subsequently, after a predetermined period has passed from time t, the etching gases, i.e., the HF gas, NHgas, and TMA gas are again supplied to the wafer W (at time t).

1 3 3 5 11 5 11 11 11 6 FIG.D If the processing from time tto just before time tis regarded as a first cycle, the processing from tto just before time tcorresponds to a second cycle, which is performed in the same manner as the first cycle, thereby etching the SiOx film. The cycle is repeatedly performed after time t, and etching progresses with each cycle. Once a desired amount of the SiOx filmhas been etched through repeating of the cycle for a predetermined number of times, the processing of the wafer W is completed (). In each cycle, the SiOx filmis etched with high uniformity between the lateral central portion and the left and right ends, resulting in a relatively high surface flatness of the SiOx filmupon completion of the processing.

7 FIG. 1 2 3 4 2 3 4 5 In addition, in each cycle, a period during which at least one selected from the group of the etching gases is being supplied corresponds to an etching period, while a period during which none of the etching gases are being supplied corresponds to an exhaust period. Accordingly, in the etching as illustrated in, periods between times tand tand between times tand tcorrespond to the etching period, and periods between times tand tand between times tand tcorrespond to the exhaust period.

11 11 5 FIG. 6 6 7 FIGS.A toD and 5 FIG. A supplementary description is provided regarding the shape of the SiOx filmafter the etching with reference to. As described above, the AFS generated from the etching gases significantly affects the shape and flatness of the SiOx filmafter the etching. When the processing is performed as described inunder conditions where generation of the AFS is prevented or the sublimability is high, the effect of the collision probability of the TMA gas becomes more pronounced, making the SiOx film more likely to assume a concave shape, as illustrated in the upper right section of.

3 3 2 3 4 5 11 11 5 FIG. Specifically, when the processing container is maintained at a relatively low pressure, a flow rate of the TMA gas supplied into the processing container is relatively high compared to a flow rate of the NHgas supplied into the processing container, the temperature of the wafer W is relatively high, and/or a period from stopping of the supply of the etching gases to a next etching gas supply (i.e., the periods between times tand tand between times tand time t) is relatively long, the SiOx filmtends to have a concave shape. Conversely, when the processing container is maintained at a relatively high pressure, the flow rate of the TMA gas supplied into the processing container is relatively low compared to the flow rate of the NHgas supplied into the processing container, the temperature of the wafer W is relatively low, and/or the exhaust period after the etching is relatively short, the SiOx filmafter the etching tends to have a convex shape, as illustrated in the lower right section of.

11 11 3 3 In other words, the surface shape of the SiOx filmafter the etching may be controlled to further increase the flatness thereof by adjusting various processing conditions, in addition to using both the amine gas and the NHgas as the etching gases. In later evaluation tests, a desirable range of the flow rate of the TMA gas relative to the flow rate of the NHgas, among the above-mentioned processing conditions, is described for improving the surface flatness of the SiOx film.

3 31 3 39 31 38 41 31 41 41 31 8 FIG. Next, an etching apparatusthat performs the etching according to the present disclosure is described with reference to a vertical cross-sectional view of. In the drawing, reference numeraldenotes a processing container included in the etching apparatus. In the drawing, reference numeraldenotes a transport port for the wafer W that is opened at a sidewall of the processing container, and is opened or closed by a gate valve. A stageon which the wafer W is placed is provided inside the processing container, and a lifting pin (not illustrated) is provided at the stage. The wafer W is delivered between the stageand a substrate transporter disposed outside the processing containerby the lifting pin.

32 41 41 32 32 41 A temperature adjusteris embedded in the stage, and the wafer W placed on the stageis temperature-adjusted. The temperature adjusteris configured, for example, as a flow path that forms a part of a circulation path through which a temperature adjustment fluid such as water flows, and the temperature of the wafer W is adjusted through heat exchange with the fluid. However, the temperature adjusteris not limited to such a fluid flow path, and may also be configured by, for example, a heater for performing resistance heating. The temperature of the wafer W (a surface temperature of the stage) when supplying the etching gases may be set to, for example, a range of −20 degrees C. to 150 degrees C., in order to perform the sublimation of AFS.

33 31 33 35 34 34 31 4 Further, one end of an exhaust pipeopens to the interior of the processing container, while the other end of the exhaust pipeis connected to an exhauster, which is configured by, for example, a vacuum pump, via a valve, which is a pressure changer. By adjusting an opening degree of the valve, an internal pressure of the processing containeris set to a predetermined pressure, and the etching is performed on the wafer W. This pressure is, for example, from 0.133 Pa to 1.3×10Pa.

46 31 41 46 51 54 51 54 61 64 50 50 61 64 50 50 46 46 46 50 61 64 A gas shower plateis provided at an upper portion of the processing containerso as to face the stage. The gas shower plateis connected to downstream sides of gas supply pathsto, while upstream sides of the gas supply pathstoare connected respectively to gas supply sourcestovia respective flow rate adjusters. Each flow rate adjusterincludes a valve and a mass flow controller. The supply and stop of each gas from the gas supply sourcestoto a downstream side are performed by opening and closing the valve included in the flow rate adjuster. Further, a flow rate of each gas supplied to the downstream side is adjusted by each flow rate adjuster. Each gas supplied to a gas flow path provided in the shower plateis discharged downward from a number of discharge ports formed at a lower surface of the shower plate. A gas supplier includes the gas shower plate, the flow rate adjuster, and the gas supply sourcesto.

2 3 2 2 2 61 62 63 64 31 46 50 31 46 31 31 A HF gas, TMA gas, Ngas, and NHgas are respectively supplied from the gas supply sources,,and, and each of these gases is supplied into the processing containerthrough the gas shower plate. The supply of each of these gases may be performed independently of each other by each flow rate adjuster. The Ngas, which is an inert gas, is supplied as a carrier gas into the processing containerthrough the gas shower platetogether with the etching gases. Further, during the execution of the above-described cycle, the Ngas is supplied into the processing containeras a purge gas even during a period in which the etching gases are not being supplied. That is, the Ngas is continuously supplied into the processing containerduring the processing of the wafer W.

3 30 30 30 30 3 3 41 46 34 Further, the etching apparatusincludes a controller, which is a computer. The controllerincludes a program, a memory, and a CPU. The program includes instructions (steps) for performing the above-described processing and transport of the wafer W. This program is stored in a computer-readable non-transitory storage medium such as a compact disk, a hard disk, a magneto-optical disk, and a DVD, and is installed to the controller. The controlleroutputs control signals to various components of the etching apparatusby using this program, and thus controls operations of the components. Specifically, examples of the operations of the etching apparatusthat are controlled in this manner include the adjustment of the temperature of the fluid supplied to the stage, the supply and stop of each gas from the gas shower plate, and the adjustment of an exhaust flow rate by the valve.

11 6 In addition, although the TMA gas is used as an amine gas in the above processing, an amine gas other than the TMA gas may also be used. Specifically, various gases of an amine compound such as dimethylamine, dimethylethylamine, diethylamine, triethylamine, monotertiarybutylamine, pyrrolidine, and pyridine may be used. Thus, any of primary, secondary, or tertiary amines may be used as the etching gas. Then, the etching gas may be appropriately selected depending on a film material of an etching workpiece. When etching the SiOx film, for example, halogen-containing gases other than HF, such as HCl, HBr, HI, and SFmay be used.

7 FIG. 3 3 Although the processing illustrated in the chart ofinvolves multiple repetitions of the cycle, the cycle may be performed only once without repetition if a required etching amount is small. Also, in the example illustrated in the timing chart, the respective gases are supplied such that a supply period of the HF gas, a supply period of the TMA gas, and a supply period of the NHgas overlap with one another, but the supply periods of these gases may not overlap. Accordingly, for example, the HF gas, TMA gas, NHgas may be supplied to the wafer W one by one in sequence. Further, two of the three etching gases may be supplied first to the wafer W, followed by the remaining one. In other words, the supply periods of only two of the three gases may overlap with each other.

11 Even if the supply periods of the three etching gases are shifted in this manner, a single cycle may be configured such that, after supplying each etching gas to the wafer W, an exhaust period during which no etching gas is supplied may be provided to sublimate the reaction products on the wafer W. That is, the SiOx filmmay be etched by repeating a cycle including an etching period during which at least one selected from the group of the three etching gases is supplied and the exhaust period following the etching period.

7 FIG. In addition, although the supply periods of the three etching gases may be shifted in this manner, it is desirable, from the viewpoint of increasing an etching rate by raising partial pressures of the etching gases around the wafer W, that the supply periods of the three etching gases overlap. It is more desirable that the three etching gases are supplied simultaneously as illustrated in(i.e., starting time points of the supply periods are the same and supply stopping time points are also the same).

3 Incidentally, it has been described that etching gases include halogen, amine, and NHas components. In the present disclosure, when an etching gas or a film as an etching workpiece is described as containing a specific component, it does not mean that the component is merely contained as an impurity, but rather that it is contained as a constituent component.

51 53 31 31 52 54 31 31 51 31 51 3 3 3 The configuration of the apparatus is arbitrary, and for example, for the gas supply pathsto, which serve as flow paths for the etching gases, tanks are interposed respectively as gas reservoirs for storing the gases, and valves are interposed respectively downstream of the tanks. By opening and closing these valves, supply of the gases from the tanks into the processing containeris switched on and off. Further, the apparatus may be configured to supply each etching gas into the processing containerat a relatively large flow rate over a relatively short period by storing the gas in the tank while the valve is closed and by opening the valve while an interior of the tank is pressurized. In addition, downstream portions of the gas supply pathsandmay be merged into a common path, and the aforementioned tank and valve may be provided in this common portion, so that the NHgas and TMA gas are stored in the common tank and supplied into the processing containerthrough the common valve. Then, as for the HF gas, to prevent unnecessary reactions with the NHgas and TMA gas, it is desirable that the HF gas be stored in a separate tank from the tank used for the NHgas and TMA gas and be supplied into the processing container. That is, the HF gas may be stored in the tank of the gas supply pathand supplied into the processing containerthrough the valve of the gas supply path.

14 11 11 12 11 12 11 12 11 14 12 11 However, the recessin which the SiOx filmis provided is not limited to being open upward (in the thickness direction of the substrate), and may also open laterally. Further, with regard to a positional relationship between the SiOx filmand the Si film, an etching amount of the SiOx filmin the region near the interface of the Si filmand an etching amount in the region relatively distant from the interface may be controlled by the present technique as long as the SiOx filmand the Si filmare adjacent to each other and both are exposed on the surface of the substrate W. In other words, the SiOx filmis not limited to being provided in the recess, the sidewall of which is formed by the Si film. In addition, the present technique is not limited to cases where both the SiOx film and another type of the silicon-containing film are simultaneously exposed on the surface of the substrate, and may also be applied to cases where the SiOx filmis provided over the entire surface of the substrate and is etched.

14 11 12 12 11 12 12 14 12 In addition, the sidewall of the recesson which the SiOx filmis provided is formed by the Si film, and as described above, it is presumed that the low adsorbability of the Si filmto the reaction products contributes to the shape of the SiOx filmafter etching. A silicon-containing film other than the Si film, such as a SiGe film, also has low adsorbability to the reaction products, and exhibits high resistance to the above-described etching gases (halogen-containing gas and basic gas), just like the Si film. Therefore, it is considered that the etching using the etching gases is effective even when the sidewall of the recessis formed by a silicon-containing film other than the Si filmsuch as a SiGe film.

The embodiments disclosed herein should be considered as illustrative and not restrictive in all respects. The above embodiments may be omitted, replaced, modified and combined in various ways without departing from the scope and spirit of the appended claims.

Evaluation tests performed in relation to the present technique are described below.

3 As Evaluation Test 1, energy amounts (ΔG/eV) required for adsorption of each of HF, NH, TMA, and AFS to silicon nitride (SiN), silicon oxide (SiO), Si, and AFS are calculated through simulation. The results are shown in Table 1. Numerical values in the table represent the respective energy amounts, with smaller values indicating higher adsorbability.

TABLE 1 SiN SiO SI AFS HF −0.21 −0.02 0.24 −0.4 NH3 0.19 0.01 0.28 −0.23 TMA 0.18 −0.05 0.31 −0.24 AFS −0.31 −0.51 0.17 −1.24

3 3 2 2 FIGS.A toD 2 FIG.D 11 12 15 11 As illustrated in Table 1, adsorbability between AFS molecules is high, indicating a tendency for the molecules to aggregate. Then, AFS and NHare easily adsorbed to SiO, but they are less likely to be adsorbed to Si. Therefore, when the NHgas is included as the etching gas, it is presumed that the reaction progresses as described inand other drawings. That is, it is conceivable that selective etching of the SiOx filmwith respect to the Si filmis performed, and that the AFS layerhas a relatively small thickness at the left and right ends of the SiOx film, as illustrated in.

3 3 6 6 FIGS.A toD 11 12 Further, TMA exhibits relatively high adsorbability to SiO but relatively low adsorbability to Si. Adsorbabilities of NHto SiO and Si are similar to those of TMA to SiO and Si. Therefore, as described in, it is observed that when both the TMA gas and the NHgas are used as the etching gases, the SiOx filmmay be selectively etched with respect to the Si film.

2 2 FIGS.A toD 3 14 14 Further, as illustrated in Table 1, SiN has higher adsorbability to AFS than Si. Accordingly, as described in, when the NHgas is used for the etching and the sidewall of the recessis formed by a SiN film, it is estimated that AFS is less likely to peel off, and the etching amount at the left and right ends is reduced. Therefore, it is considered that the sidewall of the recessmay be formed by a SiN film, but the present technique is more effective when the sidewall is formed by a Si film.

11 14 3 31 1 FIG. 7 FIG. 3 3 As Evaluation Test 2, etching was performed on the SiOx filmin the recessof the substrate having films formed thereon, as illustrated in, using a test apparatus similar to the etching apparatus, by supplying a HF gas, NHgas, and TMA gas as described in Example. The HF gas, NHgas, and TMA gas were supplied into the processing container, as illustrated in the chart of. Thus, the respective gases were simultaneously supplied to the substrate.

3 3 3 31 14 12 11 12 11 11 31 31 In Evaluation Test 2, a flow rate ratio between the TMA gas and the NHgas supplied into the processing containerwas changed for each substrate during processing. Then, SEM images of each substrate after etching were acquired and the state of the recesswas observed. Specifically, a height difference between a top of the Si filmand the lateral central portion of the SiOx film(referred to as a “central etching depth”) and a height difference between the top of the Si filmand the left and right ends of the SiOx film(referred to as an “end etching depth”) were respectively acquired. Then, an etching depth difference was calculated as the end etching depth-central etching depth. Accordingly, the smaller an absolute value of the etching depth difference, the higher the uniformity in the surface height of the SiOx film, i.e., the higher the uniformity of etching across the SiOx film surface. In the following description, a value obtained by dividing the flow rate of the TMA gas supplied to the processing containerby the flow rate of the NHgas supplied to the processing container(i.e., a ratio of the flow rate of the amine gas to the flow rate of the ammonia gas) may be referred to as the “TMA gas flow rate/NHgas flow rate.”

3 The TMA gas flow rate/NHgas flow rate was set to 11:1 in Evaluation Test 2-1, 9:3 in Evaluation Test 2-2, 7:5 in Evaluation Test 2-3, 1:1 in Evaluation Test 2-4, 5:7 in Evaluation Test 2-5, 3:9 in Evaluation Test 2-6, and 1:11 in Evaluation Test 2-7. Accordingly, the flow rate ratio is 11 (=11/1) in Evaluation Test 2-1, 3 (=9/3) in Evaluation Test 2-2, 1.4 (=7/5) in Evaluation Test 2-3, 1 (=1/1) in Evaluation Test 2-4, 0.71 (=5/7) in Evaluation Test 2-5, 0.33 (=3/9) in Evaluation Test 2-6, and 0.09 (=1/11) in Evaluation Test 2-7.

9 FIG. 10 11 FIGS.and 3 11 A graph inand images inshow results of Evaluation Test 2. The graph shows the results of Evaluation Tests 2-1, 2-3, 2-5, and 2-7 as representative examples. The horizontal axis of the graph represents the TMA gas flow rate/NHgas flow rate, and the vertical axis represents the etching depth difference, with scales provided at intervals of a predetermined numerical value (represented as “A” in the drawing). From the graph, it is seen that the absolute value of the etching depth difference in Evaluation Test 2-1 is relatively large, while in Evaluation Tests 2-3, 2-5, and 2-7, the absolute value of the etching depth difference is relatively small, indicating high height uniformity of the SiOx film.

11 11 11 11 11 3 3 3 3 Further, based on the respective images, for the SiOx film, the smaller the TMA gas flow rate/NHgas flow rate, the more the surface of the SiOx filmtends to have a convex shape, with the left and right ends lower than the lateral central portion. Then, it is seen that the larger the TMA gas flow rate/NHgas flow rate, the more the surface of the SiOx filmtends to have a concave shape, with the left and right ends higher than the lateral central portion. In Evaluation Tests 2-1 and 2-2, the SiOx filmexhibits a pronounced concave shape, and the difference between the lateral central portion and the left and right ends is relatively large, but in Evaluation Tests 2-3 to 2-7, the difference between the lateral central portion and the left and right ends is suppressed, indicating relatively high surface flatness of the SiOx film. It is particularly seen from the images that the flatness is high in Evaluation Tests 2-3 to 2-6. Accordingly, it is seen from Evaluation Test 2 that when the TMA gas and NHgas are supplied to the substrate such that the supply periods thereof overlap, it is desirable to set the TMA gas flow rate/NHgas flow rate to a value less than 3, and more desirable in a range of 0.33 to 1.4.

11 7 FIG. 3 In Evaluation Test 3, etching of the SiOx film () was performed on multiple substrates by supplying the respective etching gases as illustrated in the chart of, in the same manner as in Evaluation Test 2. In Evaluation Test 3, while keeping the TMA gas flow rate/NHgas flow rate for each substrate constant, the temperatures of the respective substrates were individually set to different values during etching. Specifically, in Evaluation Tests 3-1, 3-2, and 3-3, the temperatures of the substrates were set to 80 degrees C., 90 degrees C., and 100 degrees C., respectively.

12 FIG. Images inshow results of Evaluation Test 3. In Evaluation Test 3-3, a tendency of forming a concave shape appeared most prominently, while in Evaluation Test 3-1, this tendency was the least apparent.

11 This is believed to be due to the sublimability of AFS, as described in the embodiment. Further, in Evaluation Tests 3-1 and 3-2, the surface flatness of the SiOx filmwas relatively high. Accordingly, it was confirmed in Evaluation Test 3 that the temperature of the substrate during the etching may be less than 100 degrees C., and more particularly be equal to or less than 90 degrees C. Accordingly, it was confirmed in Evaluation Test 3 that it is desirable to make the temperature of the substrate during the etching to be less than 100 degrees C., and more particularly, to be equal to or less than 90 degrees C.

According to the present disclosure, it is possible to achieve a desired shape of an etched silicon oxide film when etching the silicon oxide film formed on a substrate.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.